Modern electronic circuits require the use of printed circuit boards for mounting and interconnecting electronic devices thereon. Typically, the various components mounted on a printed circuit board (PCB) are soldered to the board. One typical technique to solder components to a PCB consists of placing the PCB on a conveyor, and moving the PCB across a standing wave of molten solder. In recent years, for obtaining more precise control of the soldering process, infrared (IR) reflow ovens have been developed for providing a plurality of temperature zones through which a PCB passes, for causing the reflow or remelting of solder placed on the PCB prior to running it through the oven, for soldering components to the PCB. These ovens provide for closely controlled preheating of the PCB's, followed by sufficient heating in a reflow zone to cause solder on the board to reflow for soldering components, followed by a cycle of natural cool-down.
To accomplish the precise control required, for obtaining high quality soldering of components to a PCB, without delaminating the PCB material, or damaging electronic components on the board through overheating or heat stress cycling, it is important to adjust the temperature profile of the reflow oven to match the temperature profile required for the particular PCB to be soldered. To accomplish this, a large number of printed circuit boards of the same type are passed through the oven under different heating conditions, to determine the best setting of the oven for obtaining optimum soldering of the PCB. Each time a different PCB, or differently configured PCB is to be soldered, a relatively large number of identically configured PCB's must be run through the oven to obtain the optimum oven settings for soldering that configuration of PCB. Thereafter, a production run is made for soldering a large number of the identical PCB's.
During the process of obtaining the best oven settings for a particular PCB configuration, a significant number of test boards are typically scrapped. To overcome this problem, and to eliminate the time expended in test soldering PCB's, various techniques have been developed in the prior art to reduce the number of PCB's required for obtaining the best temperature profile for the setting of an oven to typically reflow solder the PCB configuration. For example, devices sometimes known as "moles", have been developed for mounting upon a PCB, to monitor various thermocouples strategically placed on the PCB, for remotely transmitting the temperature data back to a remotely located receiver, for obtaining the temperature profile of a PCB as it is passed through a reflow oven. One such temperature profile measuring system is for a flow solder system as shown and described in O'Rourke et al., U.S. Pat. No. 4,180,199.
Also, an effort has been made in the prior art to develop systems for automatically setting the controls for a reflow oven, for example, for controlling the temperature of various zones in the oven and the conveyor speed through the oven, in reflow soldering a PCB. One example of such a system is taught in Matsuo et al., U.S. Pat. No. 5,003,160. This system includes a data table for storing sets of control data relating to conveyor speed, and operating temperatures of individual heaters in specific zones of the associated oven. A microprocessor is programmed to receive conditional parameters associated with an object to be soldered, and respond by obtaining from the data table a set of control data closely associated with the combination of conditional parameters of the object. Features of the PCB, such as thickness thereof, surface area thereof, surface area of the largest component, type of material used, and the melting point of solder, are provided as input data for a PCB to be soldered, to permit the microprocessor to obtain control data from the data table for setting up the reflow oven. As indicated in column 4, lines 27 through 35 of U.S. Pat. No. 5,003,160, data stored in the data table is correlated between control data and conditional parameters associated with a plurality of objects to be soldered, respectively, for permitting the system to recognize the combination of conditional parameters associated with a given object to obtain the appropriate control data from the data table. This data is used to set up the associated reflow oven.
The present inventor recognized that there is a need in the field of the present technology for obtaining more rapid identification of control parameters for setting up an oven, such as a reflow oven, for optimizing the reflow soldering of various PCB's, without requiring the use of a very large memory for establishing a data table storing a combination of control parameters for each one of a relatively large population of different PCB boards. He also recognized the need to optimize the oven settings obtained for a specific PCB configuration, rather than use settings previously established for a PCB that has the closest match to the PCB to be soldered.